1. Field of the Invention
This invention relates to a process of producing sponge iron by a direct reduction of iron oxide-containing materials in a rotary kiln below the softening and melting points of the charge, wherein solid carbonaceous reducing agents having a high content of volatile constituents are used, oxygen-containing gases are blown through the shell of the rotary kiln at points distributed over the length thereof, the charge and the gas atmosphere are passed through the kiln in concurrent streams and hot gases are fed into the charging end of the rotary kiln by a central burner.
2. Discussion of Prior Art
The cocurrent operation of a rotary kiln used for a direct reduction affords certain advantages over a counter-current operation. If only a partial reduction to a metallization of 30 to 65% is desired, this can be effected under stable operating conditions. Additionally, a reducing coal having a smaller particle size may be used without risk that substantial quantities of unburnt carbon may be entrained out of the kiln by the exhaust gases.
A central burner at the charging end of the rotary kiln is required for the heating of the charge. As the heating rate depends on the temperature of the hot gases from the burner, said gases are supplied to the rotary kiln at the highest possible temperature although this results in a heavy wear of the lining of the rotary kiln and in a burning of carbon of the solid reducing agent charged into the charging end.
If the reducing agent charged into the charging end of the rotary kiln consists of coals having a high content of volatile constituents, the latter is expelled very quickly and is not effective for release of energy in the heating-up zone. As heat is consumed for the devolatilization, these volatile constituents increase the heat requirement in the heat-up zone so that the heat load per unit of volume in the heating-up zone increase also. These volatile constituents also result in uncontrolled combustion.
For this reason coals having a high content of volatile constituents are not charges directly into the charging end of the rotary kiln but are entrained in air which is blown from the charging end so that at least part of such coals are carried beyond the heating-up zone directly into the reducing zone (German Pat. Nos. 15 83 954 and 19 27 558). That practice, however, involves uncontrolled combustion, which results in incrustation and in damage to the shell pipes in the reducing zone.